Milling cutter



pril 29. 1924.

c3. BONNAFFOUS ET AL MILLING CUTTER 2 Sheets-Sheet 1 XFiled Aug. 13 1920 April 29, 1924.

C. BONNAFFOUS ET AL MILLING CUTTER Filed Aug. 15 1920 2 Sheets-Sheet 2 /NVENTO' CHARLES BaN/vr Frans 14 TTUPNEYS Patented Apr. 29, lgd.

UNEF@ CHARLES BONNAFFOUS AND PIERRE BOZONNET, F ST.-0UE1\T, FRANCE.

MILLING CUTTER.

Application filed August 13, 1920.

To @ZZ whom t may concern:

Be it known that we, CHARLES BONNAF- Fous and Pinnnn BoZoNNuT. manufacturers, of 36 and 38 Rue Blanqui. at St.-Ouen, Seine Department. in the Republic of France, and

citizens of the Republic of France. have invented certain new and useful Improvew ments in Milling Cutters, of which the following is a specification.

This invention relates to milling cutters which are employed for the cutting of prol les, such as gear teeth and the like. It

consists in a method whereby a special coniiguration is given to the outer surface of the milling cutter teeth for the purpose of obtaining sharpness in the cutting work performed by the teeth, facility of penetration of the teeth into the work, a good profile from the milling cutter, and conditions involving a practically constant profile of the cut surfaces whatever may be the amount of wear of the milling cutter due to successive sharpenings of the same, within certain limits.

This configuration is in principle that of a conoidal surface which is generated by a movable straight line remaining parallel to a plane perpendicular to the axis of the milling cutter but sliding on the one hand 30 upon a fixed straight line parallel .to this axis and on the other hand upon a fixed profile whose shape depends upon the profile of the work to be cut. A configuration of this kind can be readily obtained by simple mechanical means..

The accompanying drawings which are given by way of example show three forms Y of construction of this invention.

Fig. 1 is an elevation of the first form of the milling cutter. Y v

Fig. 2 is a cross-section of the same.

Figs. 3 and 4 are diagrammatic y.views showing projections of a cutter tooth upon a plane perpendicular tothe axis of the l cutter and .upon a plane parallel to the cutting face of the tooth, respectively.

, Figs. 5 to 8 are diagrammatic views similar to Fig..3 relative to different positions of the rectilinear directrix. Y Fig. 9 is a partial elevation of this cutter. showing two. consecutive teeth.

.Fig 1() is a projection. Von a plane par- .aillel to the cutting face, of the prolileof a tooth .of this 'cutter in case it were not ii@ cui;

Serial No. 403,334.

Fig. 11 is a similar projection of the profile of the tooth al of the cutter.

Fig. 12 is a similar projection of the pro file of the tooth a2.

Fig. 13 is a partial elevation of the third yform of the milling cutter.

The surface of each cutter tooth according to this invention is that of a portion of a conoid generated by a straight line a m remaining` perpendicular to the axis 0 of the cutter and sliding on the one hand upon the xed straight line t parallel to the axis 0. and on the other handvupon a fixed protile b whose shape depends upon the profile of the work to be out (Figs. 3 and 4).

In this example it is supposed that the profile b is situated in a plane o o passing through the axis o; this profile is in this case exactly similar to the desired profile of the work to be cut by the tool.

Fig. 3 indicates-besides the plane A0 c, arplane l, ,1, parallel to the latter and representing the position of the cutting face of the milling cutter after a certain number of successive sharpenings of the latter.

This plane 1, 1. gives rise in the conoid surfaceto a profile of intersection Z g, which is diii'erent from the profile ZJ. By passing along this profile a surface of revolution concentric to the axis o, this surface will intersect the radial plane o c according to a profile b1 which represents the profile of the surface out by the tooth when the latter is sharpened according to the plane 1. 1.

The following example wil-l indicate the method of proceeding in order to determine the position of the straight line a, having given the initial radius of the milling cutter. the profile b to be obtained, and the cutting angle The profile b is first drawn. Awhich is for instance symmetrical with reference to a plane perpendicular to the axis o of the cutter; parallel to o y is drawn the radius 0 c (Fig. 3), andalso the generatrix c (Z passing through cV and making the angle (5 with 0 c; kthe line 1, 1 is also drawn (Fig. y3) parallel to o c and at a distance from 0 c equal to the maximum allowable wear of the cutter tooth; the line 1, 1. will intersect c d at the point d. From o' asa center. anarc is drawnk passing through, d and intersecting 'o c yat z'.' in thiscase. c i will represent the diminution ofthe critter radius- Faoin tu@ asiat E this. ai

Mit

the line e f is drawn parallel to o 7/ and to o a' then e and f are projected upon o c (Fig. 3*) g from 0 as center anarc of a circle is drawn through f (Fig. intersecting l, L at g; lastly, a straight line is drawn through e and g which meets the extension of c al at a. This latter point belongs to the straight line a which is sought for and which is to be employed to constitute the conoid.

It Will be observed on the one hand that the points e and g of the conoid are situated in the Vsame plane parallel to the plane 0 y and on the other hand that e fz@ z', and therefore after the tooth is iyorn doivn, the radii 0 z' and 0 f of the circumference described by the `points al and g of the last cutting face Will be shorter than the radii 0 c and O e of the corresponding points `of the initial cutting face,by the samearnount, this being a necessary condition in order that the profiles cut Yby the initial cutting face containing the points c and e, ,and yby the last cutting face produced hy the last sharpening operation and containing the points (l and g, shall vbe absolutely the same, and in like manner that the profiles cut by the yintermediate cutting faces produced by successive sharpening operations parallel to 0 c shall have the constant .value such as is required under the conditions of current practice.

lt is not an essential feature that the i initial cutting face should .be'situated upon the plane 0 c .passingfthrough the axis of the milling cutter7 and .it can be located in .front or inthe rear of this plane. Neither `is .it required in order to guide the straight line a m, to make use of a directriX profile situated in the plane 0 c.y and it is evident that any other suitable profile can be vchosen which is drawn upon the conoid.

Several special cases are to be considered as regards the values which are given. as follows:

l. To the initial spacing or pitch angle such as y. at the top ogf Ithe .milling cutter.

2. To the cutting` angle of the cutting faces` such as Y 3.-Tjo rthe length of 4tooth employed in practice foi-successive sharpeningoperations with constant profile,

Fig. 5 shows the outline as indicated in Eig. 3.

The .rectilinear directrix is situated at a `finite distance in .front of the ,tOoth.

Fig. ,6 is an alternative .tonni of this outline, in which lthe rectilinear directrix (L is situated at a lignite dist-ance in front of the tooth which is greater than ,that represented in the outline of Fig. 5. A

F 7. is another alternative disposition kin which the rectilinear directriX L is located at an infinite distance in front or in the yrear of Athe tooth.

y8 is another alternative forni .in which the rectilinear directrix n, is located at a finite distance in the rear of the tooth.

In all these figures, 0 is the axis of the milling cutter, c and c are points on the profile of the initial cutting face of a tooth; Z and g are points corresponding to the points c c in the profile of the cutting face obtained by the last allowable sharpening of the tooth; c (Z is the generatriX passing through the apex of the tooth and making with the radial plane c 0 the angle corresponding to the lesired pitch; Z and g are located upon the generatrices passing through the points c and e.

All these figures relate to the same milling cutter, taking as invariable quantities the angle c 0 corresponding to the desired pitch7 and the length c rl which determines the length of tooth which can be practically ground to constant profile by successive sharpening operations effected parallel to the initial cutting face.

ln all these cases7 the surface of thc tooth is generated by a straight line parallel to a plane `perpendicular to the axis o, that is, parallel to the plane of the figure, and slid- .ing at the same time upon the rectilinear drectriX i and upon the profile c e.

In case the direction ofthe plane c c f of the initial cutting face with reference to the radial plane c o should be given, and also the position of the plane l g of the last sharpened face with reference yto the initial cutting face; lit will he possible in ,each case to determine geometrically the position to be given to the directrix (L in order to obtain the desired conditions of invariabi-lity for the profiles ofthe work to be cut. In all these casesj should .the points of the cutting profiles c @,d g. be brought upon a radial plane such as 0 .fr lby displacen'ients concentric to the axis/i, care should bc taken that c1 flzlcl (/1. lVlicn the position ofthe three points c rl yand e is known, this condition ivill alford an easy determination of the position of the fourth point (l` and the point o can be then plotted at the intersec- .tion of the extensions off? e and f/ e.

`By gradually varying the angle 0 c f from zero (Fig. 5) in the direction of the arrow, kit will he observed that the rectilinear directrix (L moves away toward the left (Fig. 6) and continuing this movement to the left to an infinite distance. it passes to an infinite distance to the right (Fig. 7) and ythen returns to a finite distance to Ythe .right (Fig. 8).

The displacements of thc position of the rectilinear directrix a are entirely due` in cach of these figures, to the value which is givcnto the angle o c Similar disf vplacements of this ,rectilinear directrix a would be occasioned by ,varying the values of the angle c 0 aa* and the length c al. 4The position of the rectilinear directrix a is therefore a function ot the values given to the angle c m, the angle o c f and the length c (Z. It will thereforebe possible to obtain an alternative form of Fig. 7 in which, for a given value of the angle c 0 .r and the length c (Z, the rectilinearI directrix a will move to iniinity when the plane containing the initial cutting face c c passes through the anis 0. The angle 0 c f will be equal to Zero.

1n the particular case in which the rectilinear directriX is situated at infinity, the surface of the tooth has the form of a cylinder either of whose profiles c Z and e g can be taken as directrix.

Milling cutters with longitudinal profile of the tooth in the rectilinear sense and conoidal surface according to the present invention possesses various points of superiority over the current types of tool. The rectilinear setting, the value of the setting angle, and the value ofthe cutting angle such as (these two angles being judiciously chosen and combined according to the case),

' will provide a sharp and a perfectly free edge for the cutting members of the milling tool and will confer upon it cutting facilities of a well-defined character. The milling cutter can therefore operate under the best conditions of speed as well as sharpness of the work produced.

The stout form of the teeth and the conoidal conformation of the tooth surface which secures the requisite constancy of the profile obtained by sharpening the front of the cutting faces, will afford means for operating under the best conditions of output regular working and durability.

According to the modification shown in Figs. 9 to 12, cut-out parts are provided in the surface of each tooth. These cut-out parts have the form of shallow grooves of either curved or rectilinear section and'disposed either parallel to the generatrices of the co-noid or in any other direction making a suitable angle with the radii of the milling cutter. The positions of these parts are alternatedor properly staggered from one tooth to the following, whereby during the whole or part of a revolution, the superposition of the partial profiles of the cutting faces operative during this rotation shall constitute the full and entire profile.

This arrangement facilitates the work of the cutter` b v reducing the developed length of cut actually effected by each tooth, and by dividing up this length into several parts whereby the chip or turning shall be broken up. For a given amount of motive power, the cutter can be given a greater forward movement per unit of time and a greater amount of penetration into the work under operation, resulting in an increased output of work as well as a practical suppression of @Jumping of the tool or' gripping in the work,-

such as is liable to occur with the full-cutting tool having teeth of continuous profile. ln the milling cutter here represented which has an even number of teeth, for inVY These cut-out parts are so disposed that the solid portions such as Zr, z', j, 7c, Z, m. (Fig. 11) and ZL', i', y", 7c", Z', m (Fig. 12) which remain after cutting away the profiles of the teeth in question, shall entirely cover the respective cut-out parts l, 2', 3', 4', 5, 6 and 1, 2, 8, 4, 5. 6 when the profiles are exactly superposed. These cut-out portions have a depth which is at least equal to the maximum thickness determined for the chip removed by each tooth per revolution of the cutting tool.

Under these conditions each tooth will remove during the work a chip which is divided into as many portions as the tooth contains full or solid parts, this affording an advantage in the milling operations, and on the other hand, since the total sum of the solid parts ZL, 2'., 7c, Z, m, and 7L', i', j', c, Z, 'm' covers the total sum of the empty spaces or cut-out parts 1', 2, 3', 4', 5, 6 and 1, 2, 8, 4, 5, 6, the traces left by the cut-ont parts of each tooth will be removed by the solid portions of the succeeding tooth; moreover, the profile cut in the work will represent exactly, and without discontinuity, the profile employed for laying out the surface of the cutter teeth (Fig.

It will also be observed that the cut-out parts which act to divide up the surface of the teeth, instead of being alternated upon adjacent teeth, can be distributed in any other suitable manner over the series of teeth, the only condition required being that the total sum of the traces or marks left by theV cut-out parts shall be entirely covered by the total sum of the solid portions.

The type represented by way of example in Fig. 13 is a combination, upon the same milling cutter, of solid teeth with the cutout teeth as herein described. The tool thus constructed has a certain number of cut-out teeth such as b1 and 7.12 (Fig. 13) and a certain number of solid teeth with continuous profile such as o3. The tool here represented Yhas a number of teeth which is a multiple of 3, or 15 teeth for instance, and contains 5 groups of 3 teeth each. constituted as follows:

One tooth of the cutout type, b1.

One tooth of the cut-out type, b2.

One tooth of the solid type with continuous profile, b3. y ln all these groups, the teeth b1 b2 b5 follow each other regulariy in the sance ori-"deinl Anv other suitable arrangement can be adopted, depending upon the number of cutter teeth, the divisibility of this number, and the predominance to be given to the solid or the cuteout teeth. Upon each tooth the cut-out parts situated on one of the sides can be disposed so as to face the solid portions situated on the opposite side or to vtace the cut-out parts of this latter side, or again, one side of the tooth can be plain and the other side provided With cut-out parts.

Claims.

l. A milling cutter whereof the teeth have the lateral faces in the form of regulated surfaces with generatriees situated parallel to a plane perpendicular to the axis of the cutter, characterized in that thesurface ot each tooth has the form of a portion of a conoid whereof the generatrices intersect a 20 directrix Whose form corresponds to the protile to be cut and arectilinear direct/rist parallel to the axis oit the cutter.

2. A milling cutter whereof the teeth have the lateral faces in the form of regulated surfaces with generatrices situated parallel to a plane perpendicular to the axis of the cutter, characterized in that the cutting face of each tooth is initially disposed in such manner that its prolongation will extend at a certain distance forwardly of the center of the cutter and is intended to be sharpened parallel to itself.

In testimony, that We claim the foregoing as our invention, We have signed our names in presence of tivo subscribing Witnesses.

CHARLES BONNAFFOUS. PERRE BOZONNET. Witnesses CLEMENT S. EDWARDS, MAURICE ROUX. 

